1. Field of the Invention
The present invention relates to a liquid crystal display unit, and in particular to an electrode terminal structure for connecting a liquid crystal display element to an external drive circuit.
2. Description of the Prior Art
Liquid crystal has an optical permeability ratio which is controllable by the applied voltage thereto. Such a characteristic has brought about its widespread use as a display unit. FIG. 1A and FIG. 1B are respectively a top view and a side view of an example of structure of a liquid crystal display element 1. On surfaces of two glass plates, i.e., an upper glass plate 2 and a lower glass plate 3, scan electrodes 5 and signal electrodes 4 and 4' respectively composing stripes are formed. Each of intersecting points formed by the scan electrodes 5 and signal electrodes 4 and 4' constitutes one picture element, and forming a liquid crystal display portion 6. Two glass plates 2 and 3 are bonded together through a spacer 7 utilizing glass fibers or the like. Into a space formed by the two glass plates 2 and 3 and the spacer 7, liquid crystal 8 is enclosed.
A prior art for connecting the above described liquid crystal display element to an external drive circuit will now be described hereinafter.
FIG. 2 shows an example of a conventional electrode terminal structure for connecting the liquid crystal display element 1 illustrated in FIG. 1A and FIG. 1B to an external drive circuit. In a conventional liquid crystal display element, it is possible to arrange one-row electrode terminals 9 as illustrated in FIG. 2 with a pitch a of approximately, 1 mm, because of a small number of display characters and hence of electrode terminals connected to the external drive circuit.
For actual connection of the liquid crystal display element 1 to the external drive circuit, a connecting member 10 is employed. The connecting member 10 is composed of insulative rubber 11 and a plurality of metal conductive pieces 12 each having .phi. of 25 .mu.m, for example, which are so arranged within the insulative rubber 1 that both ends thereof are exposed at upper and lower faces of the insulative rubber. The space between the conductive pieces is smaller than the pitch a of the electrode terminals 9 illustrated in FIG. 2. The connecting member 10 is placed on the liquid crystal display element 1 so as to be perpendicular to the electrode terminals 9 of the liquid crystal display element 1 shown in FIG. 2. On the connecting member 10, a drive circuit substrate having electrode terminals so arranged as to confront the electrode terminals 9, thereby the liquid crystal display element 1 being connected to the external drive circuit.
However, with the advance of increase in display functions and displayed contents of a liquid crystal display element, the number of electrode terminals increases greatly. In one-row arrangement as illustrated in FIG. 2, the terminal pitch a is then reduced. Accordingly, a high-precision technique is demanded for connection to the external drive circuit substrate, and leakage between terminals is apt to be incurred, causing problems in practical use.
For example, if the liquid crystal display element 1 illustrated in FIG. 1 is so small-sized as to have a diagonal line of the liquid crystal display portion 6 which is approximately 3 inches in length and each of the upper signal electrode 4 and the lower signal electrode 4' has 160 electrodes, the pitch a in the electrode terminal structure as illustrated in FIG. 2 is approximately 0.4 mm. When the liquid crystal display element is to be connected to the external drive circuit substrate through a connection which can be easily attached or removed such as a connecting member 10 as illustrated in FIG. 3, the pitch of 0.4 mm is too small to assure stable connection in practical use.
In order to eliminate the above described drawbacks, Japanese Patent Laid-Open No. 512/80 specification and Japanese Utility Model Laid-Open No. 70657/81 specification propose a liquid crystal display device wherein electrode terminals for connection to an external drive circuit substrate are arranged to form two or more rows. FIG. 4 shows a practical example of this proposal. In the practical example, electrode terminals are composed of two kinds of electrode terminals, i.e., exterior electrode terminals 13 and interior electrode terminals 14. In this case, the pitch b of the exterior electrode terminals 13 is twice the pitch a in case of one-row electrode terminal arrangement. Since the interior electrode terminal 14 is adjacent to lead wires 15 for the exterior electrode terminal 13, however, the substantial pitch b' of the interior electrode terminals is not sufficiently large. Assuming that the pitch a of the electrode terminals in one-row arrangement is 0.4 mm and the width of the lead wire 15 for the exterior electrode terminal 13 is 0.05 mm, for example, the substantial pitch b' of the interior electrode terminals 14 is 0.5 mm. As a result, the two-row arrangement has brought about only a small effect in increasing the terminal pitch.
In the electrode terminals for connection of two-row arrangement as shown in FIG. 4, a part of the lead wire 15 for the exterior electrode terminal 13 is covered by an insulative material 16 for the lead wire 15 not to be exposed, for example, as shown in FIG. 5. Thereby, the pitch of the interior electrode terminals 14 may be increased. However, this approach brings about a higher cost due to increased manufacturing processes.